Stoker and air control, including differential pressure measuring means



D. BURNS 2,490,855

F. STOKER AND AIR CONTROL, INCLUDING DIFFERENTIAL PRESSURE MEASURINGMEANS Filed Sept. 11, 1944 Dim/VD COIVTMEP sways L Y HAGNET MERCURYSWITCH INVENT OR. gawk DOA/4Z0 flue/v6.

mam W- Patented Dec. 13, 1949 STOKER AND AIR CONTROL, INCLUDINGlfiIgggENTIAL PRESSURE MEASURING Frank Donald Burns, Long Beach, Ind.,assignor to The Hays Corporation, Michigan City, Ind., a corporation ofIndiana Application September 11, 1944, Serial No. 553,491

4 Claims. 1

This invention relates to improvements in stoker controls.

One of the problems encountered in the opera tion of small underfeedstokers is that of maintaining a substantially constant fuel bed, and asubstantially constant high efliclency of operation.

In most small underfeed stokers the air supply fan and the fuel feedscrew are operated simultaneously, as by a single motor. Also, mostsmall underfeed stokers have certain fuel feed adjustments, as low,intermediate, and high, to be set to provide desired fuel-air ratios.When the device is set at low or intermediate position, and the motor isoff, a limited amount of air is continuously supplied to the combustionchamber or fuel retort according to the setting of a damper in the airsupply duct and the furnace draft. This air burns the fuel bed down whenthe stoker is oil so that upon starting, the fuel will be thinner inproportion to the off time. This will result, after the stoker has beenoff for a time, in burning of the fuel bed to a point where fi .;ures oropenings occur in the fuel bed, and the CO2 content of the products ofcombustion drops when the stoker starts. Then, when the stoker is turnedon again, the rate of flow of air is increased because the fissures inthe fuel bed have lowered the resistance to air flow therethrough. Thistends to aggravate or accelerate the condition of thinning fuel bed andimproper fuel air ratio, so that efficiency is low.

If the fuel supply motor speed is then set up one step, i. e. from lowto intermediate or from intermediate to high, the condition may bebalanced for normal operation. However, if an extreme high loadcondition is encountered, such as one requiring substantially continuousstoker operation, the new setting may prove to have overbalanced theabove described condition. In other words, the fuel may be fed at a ratefaster than it burns under the forced air supplied by the fan. This willresult in a progressive increase in the depth or thickness of the fuelbed, with resultant progressively increasing resistance to the flow ofair therethrough. If this continues, the flow of air to supportcombustion will be substantially stopped, with the result that the firemay be extinguished. However, even if combustion continues, therestriction to air flow will reduce the load carrying capacity of thestoker.

The primary object of this invention is to overcome the above describeddeficiencies and difllculties by providing means for maintaining a fuelbed of substantially constant thickness under all operating conditions.

A further object is to provide a device of this character which will socontrol a stoker as to insure maintenance of the fuel-air ratio and theCO: content of the products of combustion in a combustion unit fed bythe stoker substantially constant and at a value insuring high operatingefficiency.

A further object is to provide a control for a stoker havingindependently operated air supply and fuel feeding means wherein theoperation of the fuel feeding means is caused to respond to variation ofa condition in the air supply means.

A further object is to provide a control for a stoker havingindependently operated air supply and fuel feeding means, wherein theoperation of the fuel feeding means is controlled from variation in airflow or inthe difference in air pressure in the air supply means from apredetermined flow or pressure differential range.

A further object is to providea control for a stoker havingindependently operated air supply and fuel feeding means, which includesa ratio controller tapped at predetermined points in the air supplymeans and in the combustion chamber of the furnace associated with thestoker.

Other objects will be apparent from the description, drawing andappended claims.

In the drawing the single figure is a side view of one embodiment of theinvention, with parts shown in section and certain parts shown on anenlarged scale.

Referring to the drawing which illustrates one embodiment of theinvention, the numeral 10 40 tort and houses a feed screw (not shown)which is driven by an electric motor IS. The air supply means of thestokercomprises a fan I! driven by an electric motor l8 and having anair supply or outlet conduit l9 communicating with the bottom of theretort l2 and provided with a damper 20 therein. The construction of thestoker may be standard throughout, with the exception of the provisionof the separate motors l6 and [8. Each of these motors will preferablybe the single speed type. The fan motor l8 will be controlled by aconventional stoker control l3, such as a room thermostat, a switchresponsive to steam pressure in a boiler, or the like; and motor i6 isconnected at one terminal with said control l3.

A plate 2| or other restriction is positioned in the air supply conduitl8 between the fan I! and the damper 20, thereby providing an orifice insaid conduit. A tube 22 communicates with conduit i 9 and the side ofplate 2| adjacent the fan, and a tube 23 communicates with conduit l9 atthe opposite side of said plate 2|. Tubes 22 and 23 are connected to aconventional differential pressure measuring diaphragm unit 24. As hereillustrated diaphragm unit 24 comprises a two-part chambered housing 25having a slack diaphragm 26 clamped marginally between the housingparts. Rigid plates 21 of a size smaller than the housing chamber aresecured together to clamp the central portion of the diaphragmtherebetween, and a stud 28 is carried centrally by said plates andextends perpendicularly therefrom. One of the housing parts has acentral chambered projection 29. Stud 28 projects into and terminatescentrally in projection 29. An opening 32 is provided in one wall ofprojection 29 and is sealed by a diaphragm 33 held by a marginalclamping ring 34 secured to said projection. A lever 35 is pivoted at 36to the free end of stud 28 and extends through diaphragm 33 centrallywith a sealed fit. A pivot bracket 31 preferably supports the lever 35adjacent the diaphragm 33 to sustain the weight or stress whichotherwise would be exerted by the lever on the diaphragm. Conduits 22and 23 are connected with the diaphragm unit in communication with thechambers on opposite sides of the diaphragm 2B.

A tube 40 communicates with the air supply conduit l9 between damper 28and retort l2, and a tube 4| communicates with the combustion chamber H.The opposite ends of tubes 40 and 4| are connected to a seconddifferential pressure measuring diaphragm unit 42 of a construetionsimilar to that of diaphragm unit 24, whose parts are identified by thesame reference numerals. The two differential pressure measuringdiaphragm units are arranged in stationary close spaced relation facingeach other, preferably with their projections 29 innermost. A link 43 ispivoted at 44 to the outer ends of the levers 35 of the two diaphragmunits. This arrangement and connection constitutes the two diaphragmunits a ratio meter. A rigid arm 45 depends from one of the levers 35,being fixedly secured thereto, and mounts a permanent magnet 48 at itslower end. In its normal vertical position, the arm 45 is positioned inspaced relation to and between a fixed stop 41 and a fixedly mountedmagnetically operated mercury switch 48. Terminals 49 and 50 areprovided in switch 48, terminal 49 being located at the side of theswitch envelope at a level above the level of the mercury (not shown) inthe switch, whereby the switch is normally open when its armature is notsubjected to a magnetic influence. Terminal 50 may be grounded atTerminal 49 is connected in a circuit with the motor l9 and a source ofcurrent 52, as by means of lead 53. The circuit to motor I6 is thuscontrolled jointly by switch 48 and demand controller l3.

The operation of the device is as follows: Whenever there is a demandfor an increased rate of combustion, as at a room thermostat or at asteam pressure controlled switch, the fan motor I8 is operated, therebyincreasing the supply of air to the retort l2 and the combustion chamberH and accelerating the rate of combustion in the retort. The fuel feedmotor I6 is not controlled by demand controller l3 only, and therefore,if switch 48 is open, the motor l8 will operate independently of motor18. Operation of fan I! by motor l8 creates a pressure difl'erential induct II at the orifice or plate 2| which is transmitted by tubes 22 and23 to act upon diaphragm unit 24 of the ratio controller. Also, itcreates a pressure differential between conduit l9 and combustionchamber l I, which is transmitted by tubes 48 and 4| to diaphragm unit42 of the ratio controller. The differential pressure in tubes 48 and 41is dependent upon the thickness of the fuel bed in the retort and theresistance of the fuel bed to the passage of the air therethrough. Thetwo diaphragm units supplement each other, and the two differentialpressures are resolved in the movement of the levers 35, link 43 and arm48. If the fuel bed is thin or is fissured so that the rate of flow ofair therethrough is excessive, the arm 45 will be swung to the right asviewed in Fig. I. The magnet 46 will then be positioned close to switch48 so that the armature therein will be magnetically attracted theretoso as to close the circuit between contacts 49 and 50. In this way thecircuit to motor I8 is closed, causing fuel to be fed to the retort. Thefuel feed continues only so long as the fuel bed conditions continue ofsuch value as to position arm 45 and magnet 46 to magnetically influenceswitch 48. In other words, when the fuel bed has thickened to thedesired extent or when the fissures therein have been closed, so thatthe air flow or pressure values in the air supply line change the actionof the ratio controller and the position of magnet 48, the fuel feedmotor l6 will be deenergized without regard to whether or not the fanmotor l8 continues to operate. Under any condition other than that of anexcessively thin or fissured fuel bed, starting of the fan motor willnot cause operation of the fuel feed motor. Therefore, it is apparentthat fuel will be fed only as needed; the fuel bed will be controlled toprevent it from becoming either too thick or too thin; efficiency of theplant as evidenced by the C02 content of the products of combustion willbe maintained at a high stable level; danger of the fire beingextinguished is avoided; and adjustment of motor speed for varyingoperating conditions is not necessary.

While the embodiment illustrated and described herein includes twoseparate motors for operating the fuel feed and air supply means,respectively, it is obvious that the device may also be conditioned foroperation of both the fuel means and air supply means by a single motor.For example, the fan may have a direct drive connection with the motorand the fuel supply means may be connected with said motor by amechanical drive which includes a clutch controlled by a solenoid. Thearrangement may be such that the solenoid causes the clutch to engagewhen the controller switch 48 closes the operating circuit, butdisengages the clutch or permits disengagement of the clutch under allother conditions. It will be obvious that this single motor type drivewill operate in the same manner described above.

I claim:

1. A controller for a heating plant including a combustion chamber, astoker having air supply means actuated in response to a demandcontroller and including an air duct, and fuel feed means actuated by amotor, comprising a differential pressure measuring unit connected atopposite sides of an orifice in said air supply means, a seconddifferential pressure measuring unit connected to said air supply meansand combustion chamber, linkage connecting said units to act additivelywith each other, and means responsive to movement of said linkage forcontrolling said fuel feed motor.

2. A controller for a heating plant including a combustion chamber, astoker having air supply means actuated in response to a demandcontroller and including an air duct, and fuel feed means actuated by amotor, comprising a pair of differential pressure measuringinstrumentalities connected additively to form a ratio meter unit, anorifice plate in said air supply means, means connecting one of saidinstrumentalities with said air supply means at opposite sides of saidorifice plate, means connecting the other instrumentality with said airsupply means and said combustion chamber, and means responsive to saidratio meter unit for controlling said fuel feed motor.

3. A controller for a heating plant including a combustion chamber, astoker having air supply means actuated in response to a demandcontroller and including an air duct, and fuel feed means actuated by a.motor, comprising a ratio controller, a plurality of conduits connectingsaid ratio controller at opposite sides of a flow restriction in saidair supply means and at a third point therein, a conduit connecting saidratio controller with said combustion chamber, and means responsive tosaid ratio controller for controlling said fuel feed motor.

4. A controller for regulating the thickness of a fuel bed in a heatingplant fired by a stoker having fuel feed means actuated by a motorresponsive to a control switch and air supply means responsive to ademand controller, comprising two difierential pressure measuring units,means connecting one measuring unit to said air supply means at oppositesides of a restriction therein, means connecting the other measuringunit to said plant above and below said fuel bed respectively, and meansconnecting said units to supplement each other, said connecting meanscontrolling said switch.

FRANK DONALD BURNS.

REFERENCES CITED The following references are of record in the file ofthis patent: v

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